1. Field of the Invention
The present invention pertains to a monolithic trimmable rise and fall time generator.
2. Description of the Prior Art
To reduce the high frequency harmonic content of a transmitted signal, Mil-Std-1553 requires the output waveform to have a rise and fall time between 100 nano-sec and 300 nano-sec. This then decreases signal coupling onto adjacent cables. There is also a further requirement from some users of Mil-Std-1553, for the rise and fall time to be between 240 nano-sec and 300 nano-sec.
To produce these results, the standard approach has been to use a resistor/capacitor filter which required tight tolerance components, and therefore, necessitated a hybrid solution. The IC circuit of the present invention provides the same results with the elimination of discrete hybrid components.
Transceiver manufacturers include Data Device Corporation, and Marconi, all of which use hybrid solutions that consist of a resistor/capacitor. This technique does provide a stable rise and fall time, but to stay within the specified limits of 1553, the resistor/capacitor components must have a tight tolerance of +/-2%. This would be impractical on an integrated circuit where the components may vary as much as +/-20%.
The present invention provides a circuit which allows the rise and fall time to be trimmed to any value. A preferred operational parameter is to be in the middle of each specification (i.e., 200 ns for 1553). The trimming can be done by laser cutting a thin film resistor or selecting a different discrete resistor value on the monolith.